Automatically variable air supply control for oil burners



Feb. 14, 1950 2,497,316

J. A; LOGAN AUTOMATICALLY VARIABLE AIR SUPPLY CONTROL FOR OIL BURNERS Filed May 24, 1946 v 2 Sheets-Sheet 1- INVENTOR warp/r A. log/w BY a 6 ATTOR EYS Feb. 14, 1950 2,;197316 J. A. LOGAN AUTOMATICALLY VARIABLE AIR SUPPLY CONTROL FOR OIL BURNERS Filed May 24, 1946 2 Sheets-Sheet 2 lNV ENTOR Jmww A. 1061M Clo 5440 ATTOR EYS Patented Feb. 14, 1950 AUTOMATICALLY VARIABLE AIR SUPPLY CONTROL FOR OIL BURNERS Joseph A. Logan, Hadley, Mass., assignor to Gilbert & Barker Manufacturing Company, Springfield, Mass., a corporation oi Massachusetts Application May 24, 1946, Serial No. 672,106

4 Claims. (Cl. 158-28) The invention has for its object the provision in an oil burner of an automatically variable control of the air supply for the purpose of improving the operation of the burner by enabling greater efliciency of combustion to be secured during normal running intervals of operation of the burner, when the air fan and oil pump are running at full speed, without smoky operation during the starting and stopping intervals of operation of the burner, when the fan and pump are respectively accelerating and decelerating.

The invention is capable of general application for controlling the air supplied to mix with a spray of atomized oil, irrespective of how that spray is produced. The invention will be disclosed, by way of illustrative example, in connection with an oil burner of the type in which the spray of atomized oil is produced by a. pressure atoniizing nozzle. The application of the invention to burners having other forms of oilspray-producing means will be readily apparent from the one example disclosed.

In the accompanying drawings,

Fig. 1 is a diagrammatical view of an oil burner system with which the invention may be used;

Fig. 2 is a top view of the oil burner as arranged in front of a furnace wall;

Fig. 3 is a rear view' of the burner with part of the fan casing cut away to show one form of shutter mechanism;

Fig. 4 is a cross sectional view showing an example of a clutch for use in the burner;

Fig. 5 is a diagrammatic view indicating the system for delivering oil through the pump and pressure regulating valve; and

Fig. 6 is a fragmentary view taken similarly to Fig. 3 and showing another form of the invention.

Referring to Fig. 1, i indicates an electric inotor with a transmission 2 to drive an air supply fan 3 and an oil supply pump I0. The fan 3 blows air at a pressure of usually less than a pound per square inch through tube 5 to meet oil atomized at a very much higher pressure, for example one hundred pounds per square inch, from a nozzle 6. The air and oil mix and burn to make the flame in a combustion chamber of a heater indicated in part by the front wall I. The oil is drawn from supply tank 8 through a. pipe 9 by pump l0, and delivered through a pipe l2, and a pressure regulating valve It to a pipe II, the outlet end of which is connected to the nozzle 6. This valve maintains the oil pressure in pipe Ii and is set for the pressure necessary for the atomizing nozzle 6 to operate with good atomizing efliciency. The valve I3, the parts of which are schematically shown in Fig. 5, bypasses excess oil by a pipe ll, to the inlet side of pump III, to keep the atomizing pressure constant in pipe II, at a value determined by hand adjustment of screw l5 to vary the force of a spring I6 which bears on valve head I! and the outlet valve I8. The pump l0 works at constant speed to pump more oil than is needed at nozzle 6, the excess being by-passed through pipe H. The arrangement supplies oil to the atomizing nozzle at a constant pressure predetermined by adjustment of screw I5, no matter what size nozzle may be used, within a considerable range of nozzle sizes, each formed for a predetermined oil consumption rate. The rate of air supply is changed by an adjustable shutter, shown in other figures to be explained, in the fan inlet or outlet. The shutter is adjusted when it is desired to change the air-oil ratio for the mixture making the flame.

Such a burner system, indicated in Fig. 1, having the general nature as explained, is well known. The type of burner having this general nature, is one of the types that may be improved by this invention. Its electrical thermostat control T is merely indicated in Fig. 1, because it is so well known that it will be understood by recital of its function, i. e. to start the motor and ignition system working when heat is needed, keep the burner running until the need is satisfled, and then shut the burner down until heat is again needed, all automatically. The ignition system is represented by the electrodes 6' positioned adjacent nozzle 6. The ignition system may be turned on and oil with the motor but should at least be on when starting the burner. It is generallytrue of this burner just mentioned, that it is easy to get a clean oil fire at all times by providing a thin mixture at all times for the flame in the combustion zone. A thin mixture is one with more air than is needed to burn the oil in the mixture. A clean fire made in this easy way is known to be expensive. It does not burn the oil economically in any heating plant. The economical way to burn the oil is in a mixture having a precise and eflicient air-oil ratio, one depending on the character of the oil. The airoil ratio is usually approximated by adjusting the burner and examining the flame. Theoretically, perfection is attained when the flame mixture has no more air supplied to it than just enough to burn all the oil. Practically, a well informed man tries to make the burner operate close to the most economical air-oil ratio, but must make compromises. A flame burning with a very economical air-oil ratio, when changed by adding a little more oil to it. will smoke and by adding a little more air to it, will begin to waste oil.

The automatic operation is of great importance in the home heating plant. This general type of burner is one that is completely shut down between heating intervals. It usually operates -mtermittently even in very cold weather. The plan is to maintain approximately even house temperature by intermittent heating operation. There are many separate heating intervals each day and a great many over all the days of a full winter's heating season. Then too, it is common to use such burners with their intermittent heating operations, for domestic hot water heating plants all the year round. For each of the burner operations or cycles for heating, there is one starting and one stopping operation. Both are short operations or intervals of but a few seconds. Should the burner smoke only a little, in either of these short operations, it is likely to be overlooked, as is alsothe fact that the great number of such short smoking intervals will add up to a lot of smoke and progressive accumulation of soot on the heat transfer surfaces inside a heater. This will result in waste of oil no matter how efhciently it is burned in the long heating intervals of operation, between starting and stopping intervals. The reason will be explained later on. The problem mentioned has received some attention and burner improvements in the past have been proposed to solve it. It is the problem of this invention. The purpose of the present improvement is to provide a better solution than the prior art burners provide, all things considered.

The type of burner indicated by the diagram of'Flg. l, and the troubles with its operation just outlined, should be in mind when the specific features of improvement are described as added to a. burner for use according to this invention.

One example of such a burner with the improvements of this invention built in, is mainly shown by the top view of Fig. 2 and rear end view of Fig. 3. These figures indicate the motor i, the multi-vane fan 3 with customary vanes IS, the side extension 20 of the fan casing with a plurality of air inlet ports 2| of ample aggregate area, the oil pump It with inlet 9, the transformer 22 for the ignition system to be turned on and oil? with the motor, the pressure regulating valve 13 with regulating screw l5, its inlet pipe 12 and by-pass I 4 to pump l0, and the air tube 6 with the oil atomizing nozzle 6, mounted centrally near the end as indicated in Fig. 2 and fed by pipe II. The parts so far mentioned are well known and need no detailed description because they have been generally available in different forms on the market. The constant pressure regulating valve l3 or' means to perform its function is frequently made in various forms some of which are combined in the pump construction. The drawings show a form easy to explain for the present purpose.

The parts shown in Fig. 3, to make the improvement in the combination are seen along the I to one another and other parts of the burner, all

for a new way to automatically control the airoil ratio in the burner operation.

These particular parts added to make the improvementwill now be described. The centrifugal clutch 23 has its driving part 26 fastened to the driving portion of the transmission 2, which portion is merely an extension of the motor shaft carrying the fan rotor with blades and said driving part 26 of the clutch. The structure provides for always turning the fan 3 and the driving part of the clutch whenever the motor turns but the fan 25 and the oil pump III are sometimes stopped when the motor and fan 3 are turning. The fan 3 has the closed side of its rotor on the right and its open on the left hand, while fan 26 is reversely arranged, its closed side being on the 4 left hand.

The centrifugal clutch element per se is disclosed in my prior art Patent No. 1,985,934 of 1935 and in a similar-relation to the oil pump but not in relation to a fan 25 in a central opening through shutter 24, as I will explain later. The clutch element is described in full detail in said patent and will be only briefly described herein.

Referring to Figs. 3 and 4 for the clutch element, three driving pins 21 are fast to a disk of driving part 26. The disk 26 is not shown in Fig. 4, but is in Fig. 3. These pins 2! lie in recesses 28 in adjacent radial faces of movable clutch shoes or segments 25. When the pins 21 are rotated they rotate segments 29. The segment recesses 28, indicated in Fig. 4 permit the segments, to move in and out radially, while driving pins 27 continue to drive from one constant radial distance from th driving shaft of transmission 2. The segments are biased to their innermost position by suitable spring means, such as the garter spring 30 located in circular recesses 3| in the three segments 29. When the segments 29 are rotated at a sufliciently high speed, they are thrown outwardly by centrifugal force against the force of spring means 30 until their circumferential surfaces 32 engage the inner surface of the drum 33. the driven part of clutch 23. This occurs after the fan 3 has attained a predetermined high speed as closely as feasible to its full speed. The part 33 will then start suddenly from its rest position and be driven almost instantly at the same constant high speed as the motor. The latter will then begin to drive the oil pump I 0 of the positive displacement type, through the driven portion of transmission 2 to which said clutch drum 33 is keyed. The pump it is then given full speed without appreciable delay. When the motor current is shut oil, the transmission 2 starts to slow down and the spring 30 moves segments 29 out of driving contact with drum 33. Then the driven part of the clutch and pump I ll stop almost instantly because of the heavy load of pump l0 which load is sufficient to prevent the pump from any substantial amount of coasting. The inertia of the heavy motor rotor, which is substantial, and the inertia of the easily turned fan rotor and driving part of the clutch cause a substantial period of coasting of the driving part of transmission 2, after the motor current is switched oil. by the usual thermostat. This is the arrangement of the centrifugal clutch element. One type of centrifugal clutch per se, is indicated with its brief description but such element may be any one of many specific kinds and many are available on the 76 market, simply as centrifugal clutches.

Between the oil pump and the clutch of the Fig, 3 burner example, is the adjustable shutter 24 and the fan 25. They will now be described. The shutter 24 is a circular non-rotating disk. Its diameter is less than that of the casing extension 20, the latter being a mere casing with v enough inlets 2| through it to result as if the casing were not applied, so far as the air condition on the left of the shutter 24 is concerned. A nut 34 threaded on a screw 35 is fast or integral on the face of the shutter. Screw 35 has at its inner and outer ends unthreaded portions which have bearings in frame parts as indicated. The endbearings permit free turning of the screw. It has a slotted head 35 in a recess at the outer bearing, to be turned by a screw driver from outside of the burner. A spring 31 on the screw 35 between the frame part and a collar 33 fixed on screw 35 holds the screw in proper axial position in its bearings. When the screw is turned one way or the other by a screw driver, its threaded engagement with nut 34 on the shutter causes the latter to move axially to the right or left, because the screw 35 will merely turn and not move axially. The shutter is guided for easy adjusting movement by one or more guide pins 39, loosely passing through as indicated. In Fig. 3 a further adjustment of shutter 24 to the left, by hand turning of screw 35 one way, will make a larger inlet opening between the outer rim of the shutter 24 and the casing rim 40. A smaller opening is made by turning screw 35 the opposite way. The shutter is adjusted in this manner to provide an accurate setting of the shutter for the air inlet opening between the rim of the shutter 24 and the rim 48. This opening, thus controlled, is an annular one and theair inlet opening to the fan 3. The casing frame rim 40 of fan 3 is circular to match the circular outer rim of shutter 24. It will be clear from Fig. 3 that by turning I screw 35 by hand, the shutter rim can be made to contact rim 40, to substantially shut off any air passage between such rims. Then by turning screw 35 back, the air passage between these rims can be set with precision. The threads on screw 35 are closely pitched to enable minute variations one way or the other in the amount of such opening between these rims. This is important for minutely varying the amount of air supplied to make an economical air-oil ratio in the heating interval of the burner operation-as will be explained and then contrasted with the amount of air to be supplied in the starting and stopping intervals of burner operation. The fan 3 draws air from the left hand side of the shutter and blows it through the air tube 5 to the combustion zone.

Shutter 24 has a special opening through it to provide a supplementary air inlet to the fan casing and supply additional air to fan 3. It is a substantial central opening 4|, the edge of which is in overlying relation to the openings between the vanes 42, of auxiliary fan 25 as indicated. As shown, the sizes are such that fan 25 cannot move as much air as fan 3 when the clutch is engaged and both are operating. Fan 25 is of the multi-vane type like fan 3 but reversely arranged so as to tend to draw air from the right while fan 3 draws air from the left, both fans then turning in the same direction. Fan 25 is fixed to the driven side of the transmission 2 by a hub 43 to always turn when the oil pump turns to operate and not otherwise. The hub 43 extends from the closed side of fan 25, the other side having only an open rim connected by the many vanes 42, with openings between them. The vanes of this fan are inclined blades with horizontal edges as usual in multi-vane fans of the type indicated. They are inclined so that when the transmission 2 is driving oil pump [0,

fan 25 will always tend to draw air from the right hand side of shutter 24, and back to the left hand side and thus oppose the action of fan 3. The result is, when oil pump III is being driven, less air is supplied to the burner than when the auxiliary fan 25 is stationary. When the oil pump and auxiliary fan are at rest, the main fan 3 draws air in through the annular opening between the rim of shutter 24 and rim 40 and through the supplementary inlet formed by the spaces between the blades of fan 25. When fan 25 operates, air may still be drawn through the supplementary air inlet by fan 3 but the rate of flow will be reduced because of the opposing action of fan 25. If the fan 25 is large enough it will by-pass some of the air drawn in by fan 3 through the annular air inlet by forcing it to the left of the shutter. If the fan 25 is too small to reverse the flow throughthe central hole in the shutter 24, it will simply reduce the rate at which air flows in through this inlet. In either .case there will be the same result, a reduction in the rate of air supply to the burner when fan 25 operates. In some cases, most of the air needed for the running intervals of burner operation will be drawn through the annular air inlet, and the shutter 24 will be opened relatively wide. This will be the case when the auxiliary fan has a relatively large capacity comparable to that of fan 3. In other cases, most of the air will come through the central air inlet in the shutter 243 and the annular air inlet opening may be relatively small, as if the shutter were nearly closed. This will'be the case when the auxiliary fan 25 has a capacity much less than fan 3. But in both cases, the auxiliary fan 25 reduces the rate at which air is supplied to the burner. On starting, while the burner motor and fan are accelerating, air will be supplied at a greater rate than when the motor is operating at full seped. The same result will be obtained during the stopping interval of operation of the burner, after the oil pump ID has stopped. In the starting interval no oil is being supplied. In the stopping interval some oil may be in or reach the combustion chamber to be burned off in a thin mixture. This will be referred to again later on. The amount of excess air which will be fed to the combustion zone in the starting and stopping intervals is much more than would feed in but for the fan 25 in the shutter opening 4| to function with the clutch control as described.

Fig. 6 indicates an arrangement of the fan, the shutter, the clutch, and a fan, modified in construction and position in relation to the clutch. This example consists in building a fan rotor as part of the driven part of the clutch. The clutch elements may be the same as above described except that the clutch drum 33 on its external pe-,

-' riphery carries simple fan blades 44 which are so faced as to tend to blow air from the right to the left hand side of the shutter. The modification reduces the cost of construction. The clutch drum 33 may be provided with blades 44 in the one casting. The driven part of the clutch in this modification becomes the rotor and the motor of the fan 44. The arrangement will enable closer coupling on the line of transmission 2.

These examples show variations in detail and of course other variations can be made in the parts of the Fig. 3 burner example. Of the forms illustrated and above described, that of Fig. 6 is preferred where low cost of construction and easy installation is important. Its operating efficiency is equivalent to the form of Fig. 3. The forms of Figs. 3 and 6 may be optionally supplied with a short tubular open ended casing as indicated in Fig. 6 for the auxiliary fan.

The burner of the example described with reference to Fig. 3 is adapted to fill the combustion chamber with flowing air and in that manner condition the combustion chamber by the air movement for starting the flame. Such conditioning is accomplished before any oil is fed to start the flame. As explained, the oil pump starts suddenly, the oil then reaches the combustion at its full rate. The atomizing action starts suddenly with a full initial blast of oil and then continues for the heating interval. The result is that a flame is started by the ignition as soon as the air-oil mixture in the combustion chamber has enough oil content to burn. There is, under the conditions, plenty of air to insure a thin mixture for the initial flame as the burner starts. When started the flame will not smoke when made by a thin mixture. When the flame once starts, the continuation of the oil feeding rate and the air feeding rate quickly establishes the precise airoil ratio for the heating interval. The time interval in the transition from a thin mixture to an efllcient oil burning mixture is a short interval but long enough to accomplish the object of the desired way of automatic starting with a thin mixture and changing to an eflicient mixture for the heating interval. The air-oil ratio for the heating interval is predetermined with precision by a hand setting of the shutter 24. This varies the ratio of air flow relatively to the rate of oil flow which remains constant since the regulating valve i3 or its equivalent is set for the desired atomizing pressure. When the air shutter is adjusted for a very economical air-oil ratio for the heating interval, which is a ratio very close to one which will smoke, then the oil consumption during the heating interval is on an economical basis. The skilled man originally installing the burner should set the shutter to provide for an air-oil ratio as near as possible to one having only enough air to avoid a smoky flame during a burners heating operating interval; a setting which he may attempt by hand and eye but which may be improved by the help of known scientific instruments available for service men's use, to detect smoke and analyze the combustion gases produced by the flame. In this way the most economical use of oil in the heating interval may be attained. The improved burner is adapted to change the air-oil ratio automatically to a thin mixture ratio, at the end of the heating interval. The air-oil ratio is changed to provide more air for use in burning off any left over oil in the combustion chamber during the stopping intervals and without making a smoky flame. This change occurs as follows: When the motor I is switched off the power line, it coasts, lowers its speed and the clutch is disengaged quite near the starting of the coasting. The oil pump l and auxiliary fan stop, while fan 3 continues to coast, blowing air for the few seconds of the stopping interval. This coasting is aided in a most substantial way by disconnecting the oil pump during the stopping interval and thus avoiding its frictional drag on the coasting fan. During this slow down period much more air inlet area is provided to feed air to fan 3 to be 8 forced through tube 5 to the combustion chamber, than would be the case without the fan 28,

idle for this period in central opening ll of shut-' ter 24. The structure is arranged to get a thin mixture for the stopping interval. This is important because the oil on its way in the line from the pump to the atomizing nozzle has momentum at the time the oil pump stops. Some left over oil in. or reaching the combustion chamber needs to be burned off in the stopping interval. Fan 3 is merely coasting, the opening between the shutter rim and fan casing rim I0 is a carefully restricted opening, but the opening M is functioning as a large additional opening to provide much more air inlet area for the coasting fan to draw through the shutter and supply air to the flame in the stopping interval. This is the way any oil flame in that interval is made of a thin mixture to avoid smoking and to burn off the residual oil with a clean flame.

The conditions for the starting and stopping intervals are similar but not identical in that the extra air for starting, is to provide a thin mixture when the first full blast of atomized oil is driven into the combustion chamber for instant ignition by the sparks between electrodes 6', to start the flame, while the extra air for the stopping interval is to thin the mixture of an already established flame when it loses the full force of the oil supply but lingers on to burn oiI the oil emitted from the atomizing nozzle in weak drizzling fashion which is peculiarly liable to make smoke. It should be recognized that the active high pressure atomizing action on the oil supply helps avoid smoke in the starting period on account of the good mixture of air and oil with plenty of air supplied before the oil supply starts. This help is lost in the stopping interval. The mixture then is more liable to smoke, unless something is done with suflicient effect to avoid smoke. What is done in the example, is to supply the extra large amount of air inlet area automatically, through shutter opening 4| at the right time when the speed of fan 3 is decreasing, and when it is particularly important to have a larger inlet area.

It is useful in burners of the character here improved, to avoid a smoke flame at any interval of operation by every possible means. Even when the heating interval operation is without any smoke and the air-oil ratio is made right for the lowest oil consumption rate to generate heat economically, the oil will be seriously wasted if smoke is made in the starting and stopping operating intervals. In the use of these kinds of burners generally, there are many hundreds or thousands of these starting and stopping intervals in a heating season. A little smoke each time in one or the other or both, deposits some soot. It accumulates progressively on the heat transfer surface of the heating plant and insulates it. So even when the heating interval operation is generating heat at top efficiency so far asthe flame is concerned, the head generated efficiently will not be transferred efficiently for use because too much of it will go up the chimney. That condition means oil waste and inefficiency for the user. This is why the improved burner has been adapted to avoid smoke at any instant of its normal automatic operation.

Having disclosed my invention, I claim:

1. In an oil burner, a fan, a casing therefor having an inlet and an outlet, an oil pump, a motor connected to drive the fan, a transmission between the pump and motor, a centrifugal clutch in the transmission for driving the pump only when the fan is operating at its high speed, constant high pressure oil atomizing means to control the oil supply from the pump for meeting the air from the fan outlet, in combination with a shutter mechanism for controlling the. air at the fan inlet, said mechanism comprising an annular shutter, hand operable precision means to adjust the rim of the shutter in relation to the rim of the fan inlet opening, automatic means at the central opening of the annular shutter to control air ilow through such opening, said means comprising a supplementary fan operatively connected to the driven side of said centrifugal clutch and operable when rotating to oppose the action of the first-named fan with a tendency to move air from the inner to the outer side of the shutter when and only when the oil pump is operating, said first-named fan being operable to draw air at 'one rate through said central opening from the outer to the inner side of the shutter to supplement the air supplied around the rim of the shutter when the main fan is speeding up or slowing down in starting and stopping intervals of burner operation, said supplementary fan being operable to reduce the rate of air flow through said central opening when and only when the oil pump is operating.

2. In an oil burner, means for producing a spray of atomized oil, and means for supplying air to mix with the oil spray, the last-named means including a fan, a casing therefor having a main air inlet, a shutter to control said inlet, and precision hand-operable means to adjust the shutter and thus the efiective area of the main air inlet, said casing having a supplementary air inlet, an auxiliary fan mounted in the supplementary air inlet, and means responsive to the speed of the first-named fan for driving the auxiliary fan only after the first-named fan has acquired a predetermined high speed, the auxiliary fan when stopped enabling air to be drawn into the fan casing at one rate by the firstnamed fan through the spaces between the blades of the auxiliary fan, the latter when driven opposing the action of the first-named fan and being operable to reduce the rate of air flow through said spaces and thereby reduce the rate at which air is supplied to the oil spray.

3. An oil burner for starting, running and .stopping operations under thermostatic control,

comprising, an air supply fan, a casing for said fan having an inlet and an outlet opening, an air tube connected to said outlet opening and through which the air for combustion is supplied, an atomizing nozzle in said tube to supply oil-at a constant rate to mix with the air supplied through said tube, a pump-to supply oil to said nozzle, a motor, driving connections between the motor and fan, driving connections between the motor and pump including a centrifugal clutch operable to stop the pump except whenj the motor is operating at or above a predetermined high speed, an annular valve disc for controlling the flow through said inlet opening and having a central opening, handoperable means for effecting a precision adjustment of the rim of said disc in spaced relation to the rim of said inlet opening, and an auxiliary fan mounted in the central opening of the valve disc and connected to the driven element of said clutch to rotate when and only when the motor is operating above said predetermined speed, the auxiliary fan when stopped enabling air to be drawn into the fan casing at one rate by the firstnamed fan through the spaces between the blades of the auxiliary fan, the latter when driven opposing the action of the first-named fan and being operable to reduce the rate of air fiow through said spaces and thereby reduce the rate at which air is supplied to said tube to mix with the oil emitted from said nozzle.

4. An oil burner for starting, running and stopping operations under thermostatic control, comprising, an air supply fan, a casing for said fan having an inlet and an outlet opening, an air tube connected to said outlet opening and through which the air for combustion is supplied, an atomizing nozzle in said tube to supply oil at a constant rate to mix with the air supplied through said tube, a pump to supply oil to said nozzle, a motor, driving connections between the motor and fan, driving connections between the motor and pump including a certrifugal clutch operable to stop the pump except when the motor is operating at or above a predetermined high speed, an annular valve disc associated with said inlet opening to control the flow of air to said tube when the fan is'opcrating, said disc having a central opening therethrough, hand-operable means for efiecting aprecision adjustment of the rim of said disc in spaced relation to the rim of said inlet opening, said clutch having as its driven element a drum mounted in spaced coaxial relation in the central opening of the valve disc, and a circular series of fan blades fixed to and projecting outwardly from the periphery of said drum toward the wall of said central opening, the spaces between the fan blades providing additional air inlet area and enabling air to be drawn therethrough into the fan casing at one rate by the first-named fan, said bladeswhen rotating opposing the action of the first-named fan and being operable to reduce the rate of air flow through said spaces and thereby reduce the rate at which air is supplied to said tube to mix with the oil emitted from said nozzle.

JOSEPH A. LOGAN.

REFERENCES crrED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

